Currently (2011), commercial low-level aerial thermography
is usually carried out using helicopters eg
fly a gyro-stabilised Flir
Polytech Kelvin 350III.
This camera contains a high definition 640×480 pixel detector
that allows temperature readings either in real time or from a stored image. It
has a 0.04°C sensitivity and ±1°C accuracy. The primary advantage of this
platform is that large areas can be surveyed with precision.
For smaller areas,
light UAVs can be employed using the small Flir Tau imager range.
Our simple kite system (2011) is built around a waterproof 320 x 240
microbolometer with a 19 mm wide angle lens, giving a field of view of 36 x
320 x 240 pixel thermal imager.
This provides a resolution of a little less than the
352 x 288 pixel,
Cairnpapple, taken by James Gentles
in 2003. The sensitivity of the camera is 0.1°C but it is not calibrated
for temperature readout. The advantage of our system is that it is relatively
cheap and light. However, the total weight of the prototype rig (including camera) is 1.5kg!
Cade and John with the sandwich
box housed thermal camera and KAP rig
Wood Park, Armadale
John Wells et al., Kite Aerial Thermography,
International Society for Archaeological Prospection,
Newsletter, 29, 9-10, November 2011.
Vertical near infra-red 2008
thermal IR camera unit (£1,900 inc.VAT (2011), incorporating a window heater - 6w/2w
lithium-ion battery (£15
voltage stabiliser (£30 - this is power over-rated by an order of
PVR (£57). The original,
digital recorder was replaced by a PVR, 23 September 2011.
The rig with the new PVR (the
battery is external for safety)
The price of this
camera is outside the remit of our normally
cost-conscious work. However, we
expect the price (and weight) of handheld, thermal imagers to continue to fall in
the near future.
For simplicity, we considered
handheld, thermal IR units, but none offered this resolution,
field of view, at this price (August 2011).
Is such an approach a useful
and viable option for archaeological KAP, as the
infra-red has already proved to be? That is the question
we hope to answer. The two main considerations are (1) The
slow speed of capture of individual frames and (2) The
optimal environmental conditions for camera deployment.
is available as a free download for
using the plugin Deshaker filter (Download),
but we have not used it so far.
A HQ FF4.0 kite has been
to cope with the rig over a wider range of wind speeds. We also have
a Power Sled 81, but we are more trusting of the consistency of performance of
HQ flow forms in strong winds. Although we have not lost a camera
since we started KAP in 2007, infrequently, sleds can shear out of the sky.
Normally, this is not a problem, but it would be a disaster and
dangerous with a £2k, 1.5kg payload.
A second PathFindIR camera was
ordered in April 2012 for work on the
Scaffolding for mounting the thermal imagers at
Harnhill Manor Farm (Gloucestershire)
Royal Agricultural University
John preparing the
PathFindIR for 24 hour continuous thermography
Thermal imagers for
calibrated stills (left) and PathFindIR for 24 hour video
Dave Stott (Leeds Uni.), John
Graham Ferrier (Hull Uni.), Ant Beck (Leeds Uni.) and Tom Smith
At this point, Dave and
Ant had been taking still thermal images at intervals from the top
of scaffolding for 2x24 hours.
To reduce weight, the 60w input
(235g) has been replaced with one rated at ~10w (22g).
Input Voltage: 11.5
to 35.0 Volts
Output Voltage: 10
Line regulation: 10
Load Regulation: 12
Operating temperature: 0
65 to 150°C
The unit (CCVS3 from e-bay)
thermal overload and short
off-the-shelf voltage stabilisers are available for around £10 each. These are
solid state replacements for electro-mechanical devices used on
older cars to regulate the voltage to the control panel. The
4800mAh battery (176g) has also been replaced with a smaller one rated at
1800mAh (80g). The PVR (149g) has been replaced with a smaller,
lighter model (82g). The total weight of the rig is now 1.16kg.
Our Latest Thermal Imager
160x120 pixel Flir
Lighter and cheaper (£200 in
2015) than the PathFindIR (over £2,000)
Much has changed since 2011.
Relatively low-cost, lightweight thermal imagers (like the GoPro
Flir Duo) have made aerial
thermal imaging more accessible, especially for those using
sUAVs as an aerial platform.
Kites remain cost-effective
and are amenable to different experimental
payloads/configurations. Flight times are not battery
Flir One attached to a Leagoo
Elite 1 phone
This imager is a
vast improvement on the PathFindIR for kite work, despite
the lower resolution.
Sensitivity of the
We fly the
Flir One on a selfie stick
suspended from a kite line.
Kite with selfie stick suspended from the
Selsey Common (Gloucestershire)
Application in Archaeological Remote Sensing
do different temperatures arise on the ground?
Different materials heat up and cool down at different
rates. Such differences can be thermally imaged when
the environmental temperature changes over a short
time scale. This has been a standard approach for
delineating archaeological residues, especially in
2. You can also get temperature
differences in vegetation (http://www.univie.ac.at/aarg/aerarch/papers/Thermal.pdf)
when there is differential transpiration. Think of it
like sweating. For example, plants growing above a
wall footing have less access to moisture, transpire
less and are consequently hotter than surrounding
plants. This process can reveal crop marks throughout
the year when the relative humidity is not too high.
We have found differential drying to be the most
predictable approach. So we wait for rain and then
later head out to a site, often when a local road has
shown significant signs of drying. Longer times are
usually need around our home base in West Lothian than
around our southern base in Gloucestershire.
Visual drying of the ground is well established for
revealing archaeological residues. Looking at small
temperature changes produced by drying effectively
amplifies this phenomenon. Sometimes, drying can be
partly related to elevation as in the handheld thermogram
of the Roman amphitheatre in Cirencester
work is visible.
Timing is crucial, as can be environmental light or
With aerial thermography, in all but the driest of
climates, you do not plan to go out to a site on a
given date, the site and weather conditions tell you
on the day (even hour) when it is best to fly.
with some thermal images, we may know what variable
gives rise to the main temperature differences, but in
many cases it can be a combination of variables.
Court Playing Fields
In the visible
spectrum the field was a uniform green
The two images below were captured above a former